Field of Invention
The invention relates to a photomask and a method for manufacturing a photomask.
Related Art
In conventional photolithography, utilizing the photomask to proceed with the ultraviolet (UV) exposure on the photoresist layer is mainly classified into contact photolithography and reticle lithography.
In contact photolithography, the size ratio of the feature pattern on the surface of the photomask and the pattern actually replicated on the substrate is 1:1, and the photomask is directly very close to or nearly contacts the surface of the photoresist layer during the exposure. In reticle lithography, the size of the feature pattern on the surface of the photomask is several times of that of the pattern actually replicated on the substrate, and the exposure on the photoresist is carried out by the projection provided by an optical system.
In contact photolithography, the shading pattern on the surface of the photomask contacts and rubs against the photoresist layer on the substrate easily resulting in that the shading pattern is damaged and the lifespan of the photomask is shortened. In addition, when the surface of the substrate coated with the photoresist layer is not highly even, an uncertain gap and distance between the photomask and the photoresist layer occur and result in scattering and diffraction of light. Thus, the dimension error of the exposure is also caused and the lateral range of the exposure on the shallow portion of the photoresist layer is enlarged, so that the photoresist structure with high aspect ratio cannot be made.
Therefore, it is an important subject to provide a photomask and its manufacturing method of low cost, faster manufacturing process, relatively low operating temperature, easy manufacture, increased tightness between the photomask and the photoresist layer.